Devices are known for preventing fishing line backlash through the use of magnets. These devices have experienced problems, and as a result, have not been widely adopted. Such a device is constructed by locating magnets near the inner and outer surfaces of an electrically conductive ring. The ring is fixed to a spool shaft, and the displacement of magnetic poles by rotation of one of the magnets controls the magnetic field to adjust the brake force of the spool. Both magnet rings rotate with the spool and must be attached with prescribed clearances.
In such devices for preventing backlash, the rotation angles of the magnets are large when compared with the rotation angle of an adjustment lever. This has made it difficult to adjust the magnetic field accurately, and has caused the brake force to be difficult to control.